A conventional bead bed 1 is shown in FIG. 1 wherein a patient 2 is shown lying on the bed 1. The bed 1 generally comprises in combination a box-like bed tub 3 having a sufficient size to accommodate the patient 2 and ceramic beads 4 substantially filling the bed tub 3. The beads 4 are made, for example, of resin-coated finely divided glass having a specific gravity of approximately 2 to 3 and a particle size of 50 to 150 microns.
An air permeable filter sheet 5 is fixedly attached to the peripheral edges of the bed tub 3 to cover the upper surface thereof. The mesh of the filter sheet 5 is smaller than the particle size of the beads 4. A plenum chamber 6 is provided at the lower part of the bed tub 3 with a porous air diffusion plate 7 being located between the plenum chamber 6 and the bed tub 3. An air blower 9 is provided in a machine housing 8. The housing 8 also serves as a base for the bed. Sheet press members 10 retain the filter sheet 5 at the peripheral edges of the bed tub 3.
In such arrangement when the air blower 9 is inoperative, the beads are no longer fluidized and become stationary. The patient 2 lying on the bed at that time feels like he is resting on sand. When the air blower is operated to supply compressed air through the plenum chamber 6 and the air diffusion plate 7 to the interior of the bed tub 3, the beads 4 contained in the bed tub 3 by means of the filter sheet 5 become fluidized under the influence of the compressed air. The specific gravity of the beads 4 is lowered to approximately 1.1 to 1.2 and the patient is supported in a substantially floating state. Under such a condition, the contact pressure exerted on the patient 2 is significantly lessened and the patient feels as if he is floating in the air. After passing through the bed tub 3, the air enters the ambient environment through the filter sheet 5.
The above-described bed arrangement has the advantages that when used for medical purposes, the effectiveness of treatment is improved by restraining application of constant pressure to the affected part of the patient suffering from a burn, for example. Bedsores are also prevented on a patient under medical care for a prolonged period of time by lessening the contact pressure between the bed and the patient.
An air permeable sheet is generally used as the filter sheet 5 to cover the upper surface of the bed tub 3. Because the filter sheet 5 is air permeable, the patient's body fluids or the like are likely to permeate the filter sheet 5 and become deposited on the beads 4 in the bed tub 3. This contaminates the beads 4 and causes them to stick together and thereby deteriorating the flowability of the beads. Moreover, propagation of bacilli takes place and results in the emanation of an unpleasant odor. In the past, it has been necessary to periodically disinfect, rinse, or replace the beads 4 for hygienic purposes and such measures are inconvenient and costly.
In addition, the air supplied to the interior of the bed tub is directed upwards through the filter sheet 5 and is discharged around the patient 2. This may cause the patient discomfort. Since the air flows directly around the patient, it has been necessary to control the temperature of the compressed air supplied to the interior of the bed tub from the air blower 9 so that the air ultimately discharged around the patient is a suitable temperature.